The charged particle beam apparatus including electron microscopes employs externally applied electric and/or magnetic fields as the electromagnetic lens or deflectors which effectively and directly act on the charged particle beam (which is used as the probe) through Lorentz force or electrostatic force.
Especially in the field of electron microscopes, it is common practice to achieve a high resolution by placing a specimen in a strong magnetic field of an electromagnetic lens and employing an imaging optical system with a short focal length and limited astigmatism.
On the other hand, a specimen of magnetic material needs a device that protects it from adverse effects of magnetic fields because it is susceptible to magnetic fields externally applied by electromagnetic lenses. This object is achieved by turning off the electromagnetic lens, placing the specimen far away from the magnetic field of the electromagnetic lens, or using a magnetic shield lens that precludes the specimen from the magnetic field.
Conversely, there in an instance in which it is necessary to control the intensity and direction of the magnetic field applied to the specimen instead of avoiding the effect of the external magnetic field on the specimen. This is true for observation of superconducting magnetic flux quantum or investigation of magnetic properties of spintronics elements, in which case the mutual action of the specimen and the external magnetic field is an important parameter in experiments. Observation of a specimen in the presence of magnetic field applied thereto needs a special magnetic field application system, with the optical system for the charged particle beam taken into careful consideration, because the application of external magnetic field to the specimen, especially that in the direction perpendicular to the optical axis, causes the charged particle beam to easily deviate from the optical axis.
Japanese Patent No. 3469213, for example, discloses an magnetic field application system which is constructed such that the charged particle beam passing through the specimen describes its trajectory by deflecting systems arranged in five stages, with two each upstream and downstream the flow of the charged particle beam, symmetric with respect to the intersection of the specimen and the charged particle beam. The structure with five deflecting systems permits the specimen to receive the maximum magnetic field generated by the apparatus and also permits the charged particle beam to transmit the specimen along the optical axis in the direction parallel to the optical axis.